The production of compressed shaped articles designated as “composites” from wood pieces, fibres or particles, such as, for example, OSB (oriented strand boards), chipboards, fibreboards, such as, for example, MDF or HDF boards (medium-density or high-density fibreboards) or plywood, as well as cork boards and mouldings comprising flax, straw or other cellulose-containing materials, with isocyanate binders, optionally in the presence or absence of catalysts, auxiliaries and/or additives in an open or closed mould is disclosed in numerous patent and literature publications. See, for example, WO 98/00464, U.S. Pat. No. 5,008,359, U.S. Pat. No. 5,140,086, U.S. Pat. No. 5,204,176, and U.S. Pat. No. 3,440,189.
In these prior art processes, temperatures of 20° C. to 450° C. are necessary, depending on the binder, in order to ensure the reaction of the binders and to permit shaping of the materials to give the desired final shape, such as, for example, planks or boards. Pressures of 0 to 100 bar are reached during this procedure.
The proportion by mass of the binders, based on the total weight of the mouldings, is 1 to 80% by weight, preferably 5 to 40% by weight and in particular less than 20% by weight, depending on the type of binder used and the type of composite.
Binders used in the aforementioned prior art processes are all types of polyfunctionalized isocyanates, typically aromatic polyisocyanates. The most widely used aromatic polyisocyanate is polymeric diphenylmethane diisocyanate (PMDI). In addition to the isocyanates, various formaldehyde resins are used as binders for composite mouldings. The most common ones include urea/formaldehyde, phenol/formaldehyde or melamine/formaldehyde resins and mixtures of these. Binders comprising renewable raw materials, such as tannins, lignins or proteins, are also used in small amounts. Furthermore, casting resins, such as, for example, epoxy, polyester, polyurethane or polylactide resins, are used.
Although the production of compact cellulose/isocyanate mouldings has acquired considerable industrial importance, the prior art processes described also have technical deficiencies because of the outstanding adhesion of polyurethanes to other materials. What is particularly disadvantageous is that the mouldings adhere to the moulds and are therefore difficult to remove from the moulds, which frequently leads to damage to the mouldings, in particular to the surface thereof. In order to avoid this disadvantage, as a rule polished, metallic moulds are used and/or release agents are employed.
Either these mould release agents are used as internal lubricants in the curable cellulose-isocyanate mixture or the internal mould surfaces are provided with a uniform coating of external lubricants before the production of the mouldings, for which purpose various injection and spray methods and roll-coating methods (DE-10 337 594) are known from the prior art. It is also possible for the surface of the particles to be moulded to be coated with mould release agent. This is likewise performed by spray application.
Conventional internal or external lubricants used are, for example, fatty acids and the metal salts thereof (see, for example, WO-A-03/072324, and WO-A-02/36268), polymeric fatty acids (see, for example, EP-A-0 269 869), carboxy-functionalized siloxane (see, for example, EP-B-0 129 430), waxes (see, for example, EP-B-0 046 014), especially ester wax (see, for example, EP-B-0 057 502), oxidized wax (see, for example, WO-A-00/53381) or polyolefin wax (see, for example, WO-A-98/00464), polyolefin wax in combination with fatty acids (see, for example, WO-A-01/58998) or finally fatty acids or wax acids in combination with polysiloxanes, which are modified with an organically bonded active hydrogen group and are capable of reacting with isocyanate (see, for example, WO-A-03/008164).
Such conventional release agents have the disadvantage that the finished mouldings have dark discolorations on the surface, which greatly impair the optical value of the finished mouldings. Furthermore, compression moulds frequently show a build up of black residues.
These build-up residues can also accumulate again on the mouldings produced and in this way also lead to dark discolorations and/or irregularities in the surface structure thereof or, particularly in the case of silicone-containing release agents, can lead to considerable coating problems. As a result, an aftertreatment, such as, for example, grinding of the surface, is necessary in some cases.
DE 19601401 describes talc as a thermally stable release material in the production of shaped cellulose-isocyanate-containing articles. However, this inorganic solid is solid at the compression temperature and thus likewise leads to considerable build-up on the compression moulds.
EP 1 719 597 describes the use of siloxane compounds containing aminopropyl groups as mould release agents for avoiding the build up of black residues.
GB 1148016 describes, as release materials, organic substances which contain free hydroxyl groups, i.e., polyols, such as glycerol, ethylene glycol, polyesters or polyethers. However, because of their hydroxyl groups, these substances react with the isocyanate used as binder and cannot alone act as a substance having release activity.
DE 2932175, U.S. Pat. No. 4,257,995 and DE 3108537 describe release agents which contain acid phosphate esters as substances having release activity, in particular as internal lubricants, for use in production of (ligno)cellulose-containing products.
In the course of increasing optimization in the production of composite mouldings, there is however still a need for increasing the processing speeds and reducing the processing temperatures.